High-throughput manufacturing of epitaxial membranes from a single wafer by 2D materials-based layer transfer process

Se-mediated dry transfer of wafer-scale 2D semiconductors for advanced electronics

Two-dimensional (2D) semiconductors hold a great promise for next-generation electronics. Yet, achieving a clean and intact transfer of 2D films on device-compatible substrates remains a critical challenge. Here, we report an approach that uses selenium (Se) as the intermediate layer to facilitate the transfer of wafer-scale molybdenum disulfide (MoS2) monolayers on target substrates with high surface/interface cleanness and structural integrity. Our method enables nearly 100% film intactness of the transferred 2D semiconductors which are free from residues or contaminants. Characterizations reveal that the Se-assisted dry-transfer yields MoS2 film with superior quality compared to conventional transfer techniques. The fabricated field-effect transistors (FETs) and logic circuits based on these transferred films demonstrate remarkable electrical performance, including on/off current ratios up to 2.7×1010 and electron mobility of 71.3 cm2·V-1·s-1 for individual FETs. Our results underscore the feasibility of this dry-transfer technology for fabricating high-performance 2D electronics that are fully compatible with standard semiconductor processes, paving the way for integrating 2D materials into advanced electronic applications.

Freestanding Wide-Bandgap Semiconductors Nanomembrane from 2D to 3D Materials and Their Applications

Wide-bandgap semiconductors (WBGS) with energy bandgaps larger than 3.4 eV for GaN and 3.2 eV for SiC have gained attention for their superior electrical and thermal properties, which enable high-power, high-frequency, and harsh-environment devices beyond the capabilities of conventional semiconductors. Pushing the potential of WBGS boundaries, current research is redefining the field by broadening the material landscape and pioneering sophisticated synthesis techniques tailored for state-of-the-art device architectures. Efforts include the growth of freestanding nanomembranes, the leveraging of unique interfaces such as van der Waals (vdW) heterostructure, and the integration of 2D with 3D materials. This review covers recent advances in the synthesis and applications of freestanding WBGS nanomembranes, from 2D to 3D materials. Growth techniques for WBGS, such as liquid metal and epitaxial methods with vdW interfaces, are discussed, and the role of layer lift-off processes for producing freestanding nanomembranes is investigated. The review further delves into electronic devices, including field-effect transistors and high-electron-mobility transistors, and optoelectronic devices, such as photodetectors and light-emitting diodes, enabled by freestanding WBGS nanomembranes. Finally, this review explores new avenues for research, highlighting emerging opportunities and addressing key challenges that will shape the future of the field.

Biocomposites of 2D layered materials

Molecular composites, such as bone and nacre, are everywhere in nature and play crucial roles, ranging from self-defense to carbon sequestration. Extensive research has been conducted on constructing inorganic layered materials at an atomic level inspired by natural composites. These layered materials exfoliated to 2D crystals are an emerging family of nanomaterials with extraordinary properties. These biocomposites are great for modulating electron, photon, and phonon transport in nanoelectronics and photonic devices but are challenging to translate into bulk materials. Combining 2D crystals with biomolecules enables various 2D nanocomposites with novel characteristics. This review has provided an overview of the latest biocomposites, including their structure, composition, and characterization. Layered biocomposites have the potential to improve the performance of many devices. For example, biocomposites use macromolecules to control the organization of 2D crystals, allowing for new capabilities such as flexible electronics and energy storage. Other applications of 2D biocomposites include biomedical imaging, tissue engineering, chemical and biological sensing, gas and liquid filtration, and soft robotics. However, some fundamental questions need to be answered, such as self-assembly and kinetically limited states of organic-inorganic phases in soft matter physics.

Heterogeneous Integration of Wide Bandgap Semiconductors and 2D Materials: Processes, Applications, and Perspectives

Wide-bandgap semiconductors (WBGs) are crucial building blocks of many modern electronic devices. However, there is significant room for improving the crystal quality, available choice of materials/heterostructures, scalability, and cost-effectiveness of WBGs. In this regard, utilizing layered 2D materials in conjunction with WBG is emerging as a promising solution. This review presents recent advancements in the integration of WBGs and 2D materials, including fabrication techniques, mechanisms, devices, and novel functionalities. The properties of various WBGs and 2D materials, their integration techniques including epitaxial and nonepitaxial growth methods as well as transfer techniques, along with their advantages and challenges, are discussed. Additionally, devices and applications based on the WBG/2D heterostructures are introduced. Distinctive advantages of merging 2D materials with WBGs are described in detail, along with perspectives on strategies to overcome current challenges and unlock the unexplored potential of WBG/2D heterostructures.

A Family of Two-Dimensional Quaternary Compounds A2BXY2 (A = K, Na; B = Li, Na; X = Al, Ga, In; Y = P, As, Sb) for Optoelectronics Applications

Expanding material types and developing two-dimensional (2D) semiconductor materials with high performance have been hotspots in the field. In this research, it is found that the 12 existing semiconductors A2BXY2 (A = K, Na; B = Li, Na; X = Al, Ga, In; Y = P, As, Sb) have a pronounced layered structure. We predict their 2D structures and properties, using first-principles calculations. Lower exfoliation energies confirm the feasibility of mechanical exfoliation from their bulk phases and that the 2D structures can be stabilized independently at room temperature. Interestingly, A2BXY2 has an anionic tetrahedral one-dimensional chain or two-dimensional mesh structure of [XY2]3- composed of elements III-V. All A2BXY2 monolayers exhibit direct or indirect band gap features (0.78-1.94 eV). More encouragingly, the A2BXY2 monolayers possess ultrahigh carrier mobilities (∼105 cm2 V-1 s-1) at room temperature. Furthermore, the results based on the nonequilibrium Green's function indicate that 2D A2BXY2 exhibits a high ON/OFF ratio (∼104). To sum up, the A2BXY2 family is an outstanding promising candidate for optoelectronics application.

Route to Enhancing Remote Epitaxy of Perovskite Complex Oxide Thin Films

Remote epitaxy is taking center stage in creating freestanding complex oxide thin films with high crystallinity that could serve as an ideal building block for stacking artificial heterostructures with distinctive functionalities. However, there exist technical challenges, particularly in the remote epitaxy of perovskite oxides associated with their harsh growth environments, making the graphene interlayer difficult to survive. Transferred graphene, typically used for creating a remote epitaxy template, poses limitations in ensuring the yield of perovskite films, especially when pulsed laser deposition (PLD) growth is carried out, since graphene degradation can be easily observed. Here, we employ spectroscopic ellipsometry to determine the critical factors that damage the integrity of graphene during PLD by tracking the change in optical properties of graphene in situ. To mitigate the issues observed in the PLD process, we propose an alternative growth strategy based on molecular beam epitaxy to produce single-crystalline perovskite membranes.

Can 2D Semiconductors Be Game-Changers for Nanoelectronics and Photonics?

2D semiconductors have interesting physical and chemical attributes that have led them to become one of the most intensely investigated semiconductor families in recent history. They may play a crucial role in the next technological revolution in electronics as well as optoelectronics or photonics. In this Perspective, we explore the fundamental principles and significant advancements in electronic and photonic devices comprising 2D semiconductors. We focus on strategies aimed at enhancing the performance of conventional devices and exploiting important properties of 2D semiconductors that allow fundamentally interesting device functionalities for future applications. Approaches for the realization of emerging logic transistors and memory devices as well as photovoltaics, photodetectors, electro-optical modulators, and nonlinear optics based on 2D semiconductors are discussed. We also provide a forward-looking perspective on critical remaining challenges and opportunities for basic science and technology level applications of 2D semiconductors.

High energy density in artificial heterostructures through relaxation time modulation

Electrostatic capacitors are foundational components of advanced electronics and high-power electrical systems owing to their ultrafast charging-discharging capability. Ferroelectric materials offer high maximum polarization, but high remnant polarization has hindered their effective deployment in energy storage applications. Previous methodologies have encountered problems because of the deteriorated crystallinity of the ferroelectric materials. We introduce an approach to control the relaxation time using two-dimensional (2D) materials while minimizing energy loss by using 2D/3D/2D heterostructures and preserving the crystallinity of ferroelectric 3D materials. Using this approach, we were able to achieve an energy density of 191.7 joules per cubic centimeter with an efficiency greater than 90%. This precise control over relaxation time holds promise for a wide array of applications and has the potential to accelerate the development of highly efficient energy storage systems.

Remote Epitaxy: Fundamentals, Challenges, and Opportunities

Advanced heterogeneous integration technologies are pivotal for next-generation electronics. Single-crystalline materials are one of the key building blocks for heterogeneous integration, although it is challenging to produce and integrate these materials. Remote epitaxy is recently introduced as a solution for growing single-crystalline thin films that can be exfoliated from host wafers and then transferred onto foreign platforms. This technology has quickly gained attention, as it can be applied to a wide variety of materials and can realize new functionalities and novel application platforms. Nevertheless, remote epitaxy is a delicate process, and thus, successful execution of remote epitaxy is often challenging. Here, we elucidate the mechanisms of remote epitaxy, summarize recent breakthroughs, and discuss the challenges and solutions in the remote epitaxy of various material systems. We also provide a vision for the future of remote epitaxy for studying fundamental materials science, as well as for functional applications.

Recent Advances in Tactile Sensory Systems: Mechanisms, Fabrication, and Applications

Flexible electronics is a cutting-edge field that has paved the way for artificial tactile systems that mimic biological functions of sensing mechanical stimuli. These systems have an immense potential to enhance human-machine interactions (HMIs). However, tactile sensing still faces formidable challenges in delivering precise and nuanced feedback, such as achieving a high sensitivity to emulate human touch, coping with environmental variability, and devising algorithms that can effectively interpret tactile data for meaningful interactions in diverse contexts. In this review, we summarize the recent advances of tactile sensory systems, such as piezoresistive, capacitive, piezoelectric, and triboelectric tactile sensors. We also review the state-of-the-art fabrication techniques for artificial tactile sensors. Next, we focus on the potential applications of HMIs, such as intelligent robotics, wearable devices, prosthetics, and medical healthcare. Finally, we conclude with the challenges and future development trends of tactile sensors.

MatGPT: A Vane of Materials Informatics from Past, Present, to Future

Combining materials science, artificial intelligence (AI), physical chemistry, and other disciplines, materials informatics is continuously accelerating the vigorous development of new materials. The emergence of "GPT (Generative Pre-trained Transformer) AI" shows that the scientific research field has entered the era of intelligent civilization with "data" as the basic factor and "algorithm + computing power" as the core productivity. The continuous innovation of AI will impact the cognitive laws and scientific methods, and reconstruct the knowledge and wisdom system. This leads to think more about materials informatics. Here, a comprehensive discussion of AI models and materials infrastructures is provided, and the advances in the discovery and design of new materials are reviewed. With the rise of new research paradigms triggered by "AI for Science", the vane of materials informatics: "MatGPT", is proposed and the technical path planning from the aspects of data, descriptors, generative models, pretraining models, directed design models, collaborative training, experimental robots, as well as the efforts and preparations needed to develop a new generation of materials informatics, is carried out. Finally, the challenges and constraints faced by materials informatics are discussed, in order to achieve a more digital, intelligent, and automated construction of materials informatics with the joint efforts of more interdisciplinary scientists.

Nucleation and Growth of GaAs on a Carbon Release Layer by Halide Vapor Phase Epitaxy

We couple halide vapor phase epitaxy (HVPE) growth of III-V materials with liftoff from an ultrathin carbon release layer to address two significant cost components in III-V device - epitaxial growth and substrate reusability. We investigate nucleation and growth of GaAs layers by HVPE on a thin amorphous carbon layer that can be mechanically exfoliated, leaving the substrate available for reuse. We study nucleation as a function of carbon layer thickness and growth rate and find island-like nucleation. We then study various GaAs growth conditions, including V/III ratio, growth temperature, and growth rate in an effort to minimize film roughness. High growth rates and thicker films lead to drastically smoother surfaces with reduced threading dislocation density. Finally, we grow an initial photovoltaic device on a carbon release layer that has an efficiency of 7.2%. The findings of this work show that HVPE growth is compatible with a carbon release layer and presents a path toward lowering the cost of photovoltaics with high throughput growth and substrate reuse.

Exceptional Thermochemical Stability of Graphene on N-Polar GaN for Remote Epitaxy

In this study, we investigate the thermochemical stability of graphene on the GaN substrate for metal-organic chemical vapor deposition (MOCVD)-based remote epitaxy. Despite excellent physical properties of GaN, making it a compelling choice for high-performance electronic and light-emitting device applications, the challenge of thermochemical decomposition of graphene on a GaN substrate at high temperatures has obstructed the achievement of remote homoepitaxy via MOCVD. Our research uncovers an unexpected stability of graphene on N-polar GaN, thereby enabling the MOCVD-based remote homoepitaxy of N-polar GaN. Our comparative analysis of N- and Ga-polar GaN substrates reveals markedly different outcomes: while a graphene/N-polar GaN substrate produces releasable microcrystals (μCs), a graphene/Ga-polar GaN substrate yields nonreleasable thin films. We attribute this discrepancy to the polarity-dependent thermochemical stability of graphene on the GaN substrate and its subsequent reaction with hydrogen. Evidence obtained from Raman spectroscopy, electron microscopic analyses, and overlayer delamination points to a pronounced thermochemical stability of graphene on N-polar GaN during MOCVD-based remote homoepitaxy. Molecular dynamics simulations, corroborated by experimental data, further substantiate that the thermochemical stability of graphene is reliant on the polarity of GaN, due to different reactions with hydrogen at high temperatures. Based on the N-polar remote homoepitaxy of μCs, the practical application of our findings was demonstrated in fabrication of flexible light-emitting diodes composed of p-n junction μCs with InGaN heterostructures.

Remote epitaxial interaction through graphene

The concept of remote epitaxy involves a two-dimensional van der Waals layer covering the substrate surface, which still enable adatoms to follow the atomic motif of the underlying substrate. The mode of growth must be carefully defined as defects, e.g., pinholes, in two-dimensional materials can allow direct epitaxy from the substrate, which, in combination with lateral epitaxial overgrowth, could also form an epilayer. Here, we show several unique cases that can only be observed for remote epitaxy, distinguishable from other two-dimensional material-based epitaxy mechanisms. We first grow BaTiO3 on patterned graphene to establish a condition for minimizing epitaxial lateral overgrowth. By observing entire nanometer-scale nuclei grown aligned to the substrate on pinhole-free graphene confirmed by high-resolution scanning transmission electron microscopy, we visually confirm that remote epitaxy is operative at the atomic scale. Macroscopically, we also show variations in the density of GaN microcrystal arrays that depend on the ionicity of substrates and the number of graphene layers.

Functionalizing nanophotonic structures with 2D van der Waals materials

The integration of two-dimensional (2D) van der Waals materials with nanostructures has triggered a wide spectrum of optical and optoelectronic applications. Photonic structures of conventional materials typically lack efficient reconfigurability or multifunctionality. Atomically thin 2D materials can thus generate new functionality and reconfigurability for a well-established library of photonic structures such as integrated waveguides, optical fibers, photonic crystals, and metasurfaces, to name a few. Meanwhile, the interaction between light and van der Waals materials can be drastically enhanced as well by leveraging micro-cavities or resonators with high optical confinement. The unique van der Waals surfaces of the 2D materials enable handiness in transfer and mixing with various prefabricated photonic templates with high degrees of freedom, functionalizing as the optical gain, modulation, sensing, or plasmonic media for diverse applications. Here, we review recent advances in synergizing 2D materials to nanophotonic structures for prototyping novel functionality or performance enhancements. Challenges in scalable 2D materials preparations and transfer, as well as emerging opportunities in integrating van der Waals building blocks beyond 2D materials are also discussed.

Unveiling the mechanism of remote epitaxy of crystalline semiconductors on 2D materials-coated substrates

Remote epitaxy has opened novel opportunities for advanced manufacturing and heterogeneous integration of two-dimensional (2D) materials and conventional (3D) materials. The lattice transparency as the fundamental principle of remote epitaxy has been studied and challenged by recent observations defying the concept. Understanding remote epitaxy requires an integrated approach of theoretical modeling and experimental validation at multi-scales because the phenomenon includes remote interactions of atoms across an atomically thin material and a few van der Waals gaps. The roles of atomically thin 2D material for the nucleation and growth of a 3D material have not been integrated into a framework of remote epitaxy research. Here, we summarize studies of remote epitaxy mechanisms with a comparison to other epitaxy techniques. In the end, we suggest the crucial topics of remote epitaxy research for basic science and applications.

Understanding the 2D-material and substrate interaction during epitaxial growth towards successful remote epitaxy: a review

Remote epitaxy, which was discovered and reported in 2017, has seen a surge of interest in recent years. Although the technology seemed to be difficult to reproduce by other labs at first, remote epitaxy has come a long way and many groups are able to consistently reproduce the results with a wide range of material systems including III-V, III-N, wide band-gap semiconductors, complex-oxides, and even elementary semiconductors such as Ge. As with any nascent technology, there are critical parameters which must be carefully studied and understood to allow wide-spread adoption of the new technology. For remote epitaxy, the critical parameters are the (1) quality of two-dimensional (2D) materials, (2) transfer or growth of 2D materials on the substrate, (3) epitaxial growth method and condition. In this review, we will give an in-depth overview of the different types of 2D materials used for remote epitaxy reported thus far, and the importance of the growth and transfer method used for the 2D materials. Then, we will introduce the various growth methods for remote epitaxy and highlight the important points in growth condition for each growth method that enables successful epitaxial growth on 2D-coated single-crystalline substrates. We hope this review will give a focused overview of the 2D-material and substrate interaction at the sample preparation stage for remote epitaxy and during growth, which have not been covered in any other review to date.